Butterflies Copy Their Neighbors To Fool Birds

August 15, 2011

The mystery of how a butterfly has changed its wing patterns to mimic neighboring species and avoid being eaten by birds has been solved by a team of European scientists. The study was published August 14, 2011 in the journal Nature.

Funded by the Biotechnology and Biological Sciences Research Council (BBSRC), the study focused on the Amazonian species Heliconius numata, which mimics several other butterfly species at a single site in the rainforest. One population of Heliconius numata can therefore feature many distinct wing color patterns resembling those of other butterflies, such as the Monarch’s relatives Melinaea, which are unpalatable to birds. This acts as a disguise, protecting them against predators.

The researchers located and sequenced the chromosomal region responsible for the wing patterns in H. numata. The butterfly’s wing-pattern variation is controlled by a single region on a single chromosome, containing several genes which control the different elements of the pattern. Known as a ‘supergene’, this clustering allows genetic combinations that are favored for their mimetic resemblance to be maintained, while preventing combinations that produce non-mimetic patterns from arising. Supergenes are responsible for a wide range of what we see in nature: from the shape of primrose flowers to the color and pattern of snail shells.

The researchers found that three versions of the same chromosome coexist in this species, each version controlling distinct wing-pattern forms. This has resulted in butterflies that look completely different from one another, despite having the same DNA.

Professor Richard ffrench-Constant of the University of Exeter added: “This phenomenon has puzzled scientists for centuries ““ including Darwin himself. Indeed, it was the original observations of mimicry that helped frame the concept of natural selection. Now that we have the right tools we are able to understand the reason for this amazing transformation: by changing just one gene, the butterfly is able to fool its predators by mimicking a range of different butterflies that taste bad.”

This single supergene also appears important in melanism in other species, including moths. In April 2011, a team led by Liverpool University explained in the journal Science how the Peppered Moth developed its black wings in nineteenth-century Britain’s sooty industrial environment.

“This supergene region not only allows insects to mimic each other, as in Heliconius, but also to mimic the soot blackened background of the industrial revolution ““ it’s a gene that really packs an evolutionary punch,” added Professor Richard ffrench-Constant.